There is a limitation when running a standalone BizTalk360 server and you have rules with .Net classes as part of the vocabulary of the rules. In this cases you may receive this error "Unable to locate assembly AssemblyName" when navigating to Business rules. You have to make the assemblies available in the GAC of that standalone server for the Rule Engine shared components to be able to load the required types and show the relevant UI.
Add the required assemblies directly to the Global Assembly Cache (GAC) or install the application packages (MSI, etc) where the .Net vocabulary resources are contained.
If you are using the ESB Toolkit a policy contains rules with .Net vocabularies and in this case the ESB Toolkit MSI should be installed. The installer can be found on the BizTalk media located at (BizTalk Server\ESBT_x64\BizTalk ESB Toolkit 2.2.msi).